DocsUI M3: Duplicate menu folder for flag material3 enabled

This is a preparation to customize the app bar for Material3 because it
used menus.

Test: Manual build, deploy apk and start it on DUT with flag on
Flag: com.android.documentsui.flags.use_material3
Bug: 377771271, 377771946
Change-Id: I87a39689b21a00b51057811db17f37358cc3b050